Science Saturday: Paleosols
Paleosol literally means "ancient soil." In geology and paleontology, a paleosol is a former soil preserved by burial under alluvium, loess or volcanic deposits.
Paleosols are frequently used to help determine the climate when they were deposited.
Figure 4. Photos illustrating paleo-Vertisol features in the Yellow Cat Member at Poison Strip, Utah (Figure 1; PS), where local conditions have maintained exceptional paleosol exposures of far greater quality than those at Utahraptor Ridge (Figure 3). (a) Two stacked paleosols (ps1, ps2); ps1 contains several carbonate-filled cracks (horizontal white arrows), and ps2 exhibits a zone of prominent, filled soil cracks (sc). Pathways of the downward translocation of sandier soil material from above into clayey soil material below are shown for selected cracks as yellow arrows at the left. (b) Closeup of soil cracks (sc) in ps2. (c) Another paleosol (ps) with prominent slickensides, identified by diagonal white arrows; general sense of shear along slickensides is shown by yellow arrows. Shear within this Early Cretaceous soil profile moved materials obliquely up and down. Features shown in these photographs suggest that perfect stratigraphic superposition (e.g., of paleosol organic matter and volcanogenic zircons) is very unlikely to exist within these paleosol profiles due to ancient pedoturbation. We propose that conditions were similar at Utahraptor Ridge during the Early Cretaceous (see text for further discussion).
A vertisol is a swelling clay soil. Swelling clays have a significant amount of ash in them which causes them to expand when wet. These clays tend to be incredibly sticky, adding 10 pounds to your feet in minutes. This indicates that there was likely some active volcanism during the early Cretaceous.
Paleosols can also be used to reconstruct paleo atmospheres. Oxidized paleosols like the red clay in the photograph above could indicate a rise in atmospheric oxygen.
Paleosols often contain fossilized pollen which tells a lot about ancient ecosystems.
Who knew old dirt could be so informative!
