Roots and fossil root casts at East Turkana, Kenya, are valuable as paleo-environmental indicators. Roots are preserved within the Koobi Fora Formation as calcified concentric and nodular casts in lithologies independently interpreted as fluviodeltaic or lacustrine-coastal plain. Five common root cast "types" are recognized: (1) horizontal, planar root mats; (2) vertical or vertically branching root structures; (3) horizontal or horizontally branching root structures; (4) diagonally branching root structures; and (5) root clusters or balls. Root mats are usually in blocky or laminated muds. Typically, the mats extend laterally over tens of square meters, although an individual mat will be only about 5 cm thick. They appear to have grown in quiet-water lagoons. Vertical ro t structures are best developed in coarse-grained sands interpreted as fluvial channel, and secondarily in fine-grained silts believed to be interdistributary overbank deposits. They are uncommon in blocky or laminated lagoonal muds. Comparison of root morphologies among living East Turkana plants supports interpretation of the fossil associations. In arid environments water availability is a dominant factor in root morphology. Plants growing along intermittent streams or flood plains must frequently rely on perched water bodies or underground seepage, and therefore send out long vertical tap roots to take advantage of this limiting resource. Plants living within shallow reed swamps have no such requirement, as their roots are nearly continually immersed in ground water; during floods th plant stalk itself is subaqueous. The roots of these plants tend to extend laterally in thin mats over much of the lagoon.

End_of_Article - Last_Page 434------------