Geologist here. This reminds me of the previous story about massive paleoburrows (also in Brazil) that are thought to have been dug by extinct giant ground slot

Geologist here. This reminds me of the previous story about massive paleoburrows (also in Brazil) that are thought to have been dug by extinct giant ground sloths [1,2]. The geological background for both of these stories seems to be that certain types of iron-rich soils ("cangas") found in South America have been found to erode extraordinarily slowly [3], in part because the iron oxides recrystallize to form a hard surface known as a duricrust [4]. This slow erosion combined with deep chemical weathering leads to old, thick soils that can hold a lot of ancient surprises. [1] https://news.ycombinator.com/item?id=18236249 https://news.ycombinator.com/item?id=18236249 [2] http://blogs.discovermagazine.com/crux/2017/03/28/paleoburrows-south-america/ http://blogs.discovermagazine.com/crux/2017/03/28/paleoburro... [3] https://www.sciencedirect.com/science/article/pii/S0012821X1200101X https://www.sciencedirect.com/science/article/pii/S0012821X1... [4] https://www.sciencedirect.com/science/article/pii/S0016703714000805 https://www.sciencedirect.com/science/article/pii/S001670371...