Field, micromorphologic and geochemical study of modern and ancient soils from Riesel, Texas and Rusinga Island, Lake Victoria, Kenya.




Michel, Lauren Ashley.

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Paleosol are utilized to reconstruct paleoclimate and paleoenvironment by paleopedologists. However, paleopedologists must constrain for all of the state factors that create a soil before paleoclimate or paleoenvironment can be assessed. Study of a modern catena in Riesel, TX shows that landscape position, parent material and time have important implications for pedogenesis. Soils with a limestone parent material component that form on ridge crests-side slopes may include marine bedrock within their pedogenic calcite nodules, because soil erosion rates exceed soil-production rates. Conversely, soils that form on toe slopes have a longer period of soil duration and formation, and more complete weathering of the parent material occurs. These soils have pedogenic carbonate nodules that reflect an admixture of CO₂ from the atmosphere and soil-derived CO₂. Since the initial discovery of Proconsul, Rusinga Island has been one of the most important Early Miocene fossil localities in East Africa, with vertebrate, invertebrate, and plant fossils recovered. Because environment is a catalyst for evolutionary adaptation, scientists have attempted to determine the paleoenvironment in which Proconsul lived. However, paleoenvironmental reconstructions have lead to conflicting results, with interpretations ranging from open grassland/parkland to closed-canopy rainforests. Recent revised stratigraphy, coupled with new paleomagnetic data and age dates, allows for a unique opportunity to reconstruct paleoenvironment for a time-slice of Miocene strata on Rusinga Island that contains both Pronconsul and the catarrhine Dendropithecus, among other vertebrate fossils. Paleopedological study has indicated the existence of a forest ecosystem developed on a landscape that received frequent inputs of sediment reworked from volcaniclastic materials. Global Positioning System mapping of fossil tree stump casts has allowed for modern forestry metrics to be applied whereas description of root cast density and structure, and paleosol descriptions have provided insight for below-ground processes. Although traditional paleosol-based proxies fail because of the lack of time for pedogenic development, paleobotanical proxies applied to fossil leaves in the overlying sandstone are able to constrain mean annual temperature and mean annual precipitation. Using this multi proxy approach, a higher-resolution picture has emerged that ties Proconsul definitively to a multistoried, closed-canopy, tropical seasonal forest that was probably relatively wet, and hot.



Michel, L. A., Driese, S. G., Nordt, L. C., Breecker, D. O., Labotka, D. M., Dworkin, S. I. "Stable-Isotope geochemistry of vertisols formed on marine limestone and implications for deep-time paleoenvironmental reconstructions." Journal of Sedimentary Research 83, (2013): 300-308.
Michel, L. A., et al. "Paleopedological and geochemical interpretation of a late early miocene paleoforest time-slice, Upper Hiwegi Formation, Rusinga Island, Lake Victoria, Kenya." Palaios (submitted).
Michel, L. A., Peppe, D. J., Lutz, J. A., Driese, S. G., Dunsworth, H. M., Harcourt-Smith, W. E. H., Horner, W. H., Lehmann, T., Nightingale, S., McNulty, K. P. "Remnants of an ancient forest provide ecological context for early miocene fossil apes." Nature Communications, 5 (2014): 3236, doi:10.1038/ncomms4236