Robert E. Lamond¹, A. A. Ekdale¹

(1) University of Utah, Salt Lake City, UT

ABSTRACT: Paleoenvironmental Controls of Non-marine Ichnofacies and Ichnofabrics in the Plio-Pleistocene Turkana Basin, Northern Kenya

Diverse, recurrent associations of trace fossils (ichnofacies) and biogenic sedimentary fabrics (ichnofabrics) occur in fluvial and lacustrine sandstone, mudstone and limestone facies of the Plio-Pleistocene Nachukui Formation in the Turkana Basin of northern Kenya. The trace fossiliferous strata represent facies ranging from ephemeral, braided and meandering stream paleoenvironments to lake margin beach, lagoon and shallow offshore paleoenvironments. The stratigraphic record here reflects an extremely dynamic paleogeography characterized by numerous transgressions and regressions of vast lakes that occupied this region during the past four million years. Ichnologic information refines our understanding of the paleoenvironmental and paleogeographic fluctuations that occurred in the Turkana Basin, which is of extraordinary interest because of the very significant fossils of human ancestors (both Australopithecus and Homo) that have been discovered here.

While locally abundant and well-preserved, trace fossils are sparsely distributed stratigraphically and spatially throughout the Turkana Basin. Although individual ichnofacies typically exhibit low diversities consisting of only a few ichnogenera, there are many different ichnofacies and ichnofabrics preserved, representing the various paleoenvironmental settings. The environmental factors that control the distribution of the trace fossils include sediment composition and texture, type of depositional environment, current and/or wave energy, water chemistry and water saturation of the sediment. Seven local, paleoenvironmentally controlled ichnofacies can be recognized: Termitichnus, Taenidium-Palaeophycus, Skolithos-Arenicolites, Teichichnus, Sertaterebrites, Lockeia and Piscichnus ichnofacies. In addition, several distinctive ichnofabrics, including mammal trample beds and rhizolith-rich beds, can be discerned.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado