Sedimentological, geochemical, and biological aspects of bisequal spodosols formed on Trail Ridge, south Georgia, USA

Bisequal spodosol profiles occur on most of the higher and older marine terraces of the Georgia Coastal Plain. Profiles representative of the Mandarin series along Trail Ridge typify the podzolization process in which both organic matter and aluminum are leached from upper horizons and precipitated in dense humate or "spodic" horizons. Dramatic changes are evident in bulk density, particle size, pH, and organic matter measured by loss-on-ignition (LOI) between each of several spodic horizons and the overlying elluvial ("E") horizons. While the extremely low pH values in the E horizons may explain much of the translocation of aluminum and organic molecules, fungi and other organisms also appear to have played a significant role in the genesis of these soils. Results from thin-section petrography and examination under a scanning electron microscope (SEM) provide tentative support for the hypothesis that organisms are themselves contributing to an alternating pH between E and Bh horizons as well as other chemical and sedimentological changes in these soils. A minimum age estimate of 0.1 - 0.5 ka for spodosol formation is indicated by locations where agriculture and forestry have disturbed the surface horizons. Soil formation began on Trail Ridge at least as early as the last interglacial period, 75-125 ka.