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theses

Reconstruction of paleoenvironmental and paleoclimatic conditions is an important part of the interpretation of geological records, especially for deposits associated with fossils or cultural remains. This study presents a high resolution reconstruction of a ~1.3 Ma paleowetland in Olduvai Gorge, Tanzania, based on facies architecture, composition, clay mineralogy, grain size, stable isotopes, and biological remains (diatoms and phytoliths). Outcrops of a siliceous silt/carbonate packet were mapped over a distance of 1.5 km; stratigraphy was exposed in ten 1-3 m deep trenches. Five facies are identified and form the stratotype: sandy silt, siliceous earthy silt, carbonate, waxy sandy silt, and brown silty clay. The environment of deposition was a wetland with localized distributary channels formed at the distal end of a fluvial plain and margin of a saline-alkaline playa lake. The sequence starts with a sandy silt deposited as terminal splay delta or playa lake margin sands. The wetland sequence overlies this sandy silt and consists of a siliceous earthy silt (and local brown silty clay deposits) and an overlying carbonate. Phytoliths and diatoms record a biologically rich environment. The carbonate contains freshwater fossils and has a stable isotope signature reflecting meteoric source water. The sequence is capped with waxy sandy silts deposited as the playa lake expanded and drowned the wetland. The sequence records the effects of a rising water table related to more positive water budget (dry to wet portion of a Milankovitch precession cycle). This wetland was a persistent source of freshwater on the landscape for thousands of years. It would have provided a useful source of both food and water for the two species of hominin found in Olduvai at this time – Homo erectus and Paranthropus boisei.

ETD_7834

M.S.

Includes bibliographical references

by Kevin R. Garrett

doi:10.7282/T3T43WJ0

ETD graduate

The author owns the copyright to this work.