Cenozoic Climate
• How do we know that Oligocene climate changed from tropical to semi-arid?
• Mudstones = paleosols (ancient soils)
• What is a soil?
Soils
• soil = upper part of the regolith or pedosphere that supports life
• Components = what is in soil…..
• Sediment (Sand, silt and clay)
• Organics (litter & humus)
• Organisms
• H2O, gasses, & nutrients
Soils
• The result of weathering rock and sediment in place
• Important Processes
• Mechanical and chemical weathering
– Sediment and Clay minerals
• Activities of plants, microbes, and invertebrates
Soils
• Factors - parent, climate, time, topography, and organisms
• Most important = Climate
Soils
• Climate determine thickness and characteristics of the soil profile
• Topsoil
– Organics and sediments
– leaching
• Subsoil
– Sediments and minerals
– Accumulation
• Parent
Soil Classification
• Factors - parent, climate, time, topography, and organisms
• Oficial USDA system - 12 orders
Temperate Soils
• Temperate = thick, organic rich topsoil, moderate leaching
Arid Soils
• Arid = thin topsoil, mineralization in the subsoil, soil calcite - caliche
Tropical Soils
• Tropical = poor topsoil (decay in the tropics is very efficient), intense
leaching and accumulation of iron and aluminum oxides
Paleosols
• An ancient buried soil
• How do you recognize them? - they have been altered (rock)
• Evidence of life
– Root traces and trace fossils
– bioturbation
• Traces of horizons and structures
– blocky texture
– Color, caliche,
White River Paleosols
• Yellow Mounds = mineralized tropical soil
• Chadron Paleosols - soil supporting a dense forest - plant fossils
• Brule and Sharp Paleosols - soil supporting a savanna - fossils, burrows,
and caliche (soil carbonate)