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Perturbation (from Latin: perturbare "to confuse, disorder, disturb," from per- "through" + turbare "disturb, confuse," from turba "turmoil, crowd") is a set of Pedology (soil study) and sedimentary geology processes relating to changes in the nature of water-borne alluvial sediments and in situ soil deposits over time.
- Pedoturbation (from Greek: πέδον, pedon, "soil") refers to perturbation that is not caused by illuviation (re-distribution by water.) In clay soils, for instance, humifaction causes expansions and contractions which severely deform the alluvial accumulations. Formation of new pedological compounds, such as carbonate precipitation also causes fragmentation and disorganisation, as does frost weathering (cryoclastia, gelifracción or gelivación) in cold climates. Field termites are especially important in tropical climate regions within 15° of the equator.
- Bioturbation is the displacement and mixing of sediment particles (i.e. sediment reworking) and solutes (i.e. biologically-mediated irrigation) by benthic zone (bottom water) fauna (animals) or flora (plants). Activity of bacteria is yet another important cause of perturbation in the geological record.