TitlePaleoenvironmental and paleoclimatic reconstruction of a Pleistocene catena using paleopedology and geochemistry of lake margin paleo-Vertisols, Olduvai Gorge, Tanzania
NameBeverly, Emily Jane (author), Ashley, Gail M. (chair), Feibel, Craig S. (internal member), Driese, Steven G. (outside member), Rutgers University, Graduate School - New Brunswick,
Sediments (Geology)--Tanzania--Olduvai Gorge,
Olduvai Gorge (Tanzania)--Antiquities
DescriptionOlduvai Gorge, Tanzania (3°S) contains a rich record of Pleistocene paleoclimates and paleoenvironments, as well as an abundance of paleontological and archaeological data. The 2.2 Ma of volcaniclastic infill can be divided into time-slices using dated tuffs. Until ~1.75 Ma the sediments were deposited in a semi-arid, closed rift basin that contained a shallow saline-alkaline lake that fluctuated periodically with climate, depositing sediment on the lake margin. Four trenches that range in thickness from 2 to 2.5 m in a ~1 km transect of the lake margin flat were described and sampled. This ~20 ka time-slice between Ng’eju Tuff and Tuff IF (~1.785 Ma) contains both stacked and cumulative paleosols that are interpreted as a heterogeneous paleocatena. Closer to the lake, these paleosols are thinner, vertically stacked, and separated by thin tuffs or tufa. Further from the lake margin, there is additional volcaniclastic input, and the paleosols are thicker and cumulative. Macroscale and micromorphological features identify these clay-rich paleosols as paleo-Vertisols. Abundant pedogenic slickensides and a variety of ped shapes were observed in the field as well as micro-ped structures and stress cutans in thin section. Although weakly developed, these paleo-Vertisols also have distinct horizons defined by soil color changes, differing ped shapes, and bulk geochemistry. Eighty samples from the paleosols and parent materials were analyzed for bulk geochemistry of major, rare, and trace elements. Geochemical proxies reveal a climosequence not definitively identifiable in the field or in the micromorphology. Molecular weathering ratios show increased weathering, and mass-balance calculations indicate greater translocations (positive and negative) through time. It is likely that lower soil moisture due to a drier climate created better-drained conditions allowing for increased pedogenesis. Mg oxides and zeolites precipitating in rhizoliths are further evidence for changing redox conditions and water chemistry, likely due to increased aridity. The drying trend in this climosequence is consistent with faunal, stable isotope, and lithostratigraphic records within Olduvai Gorge and with marine dust records from northern Africa. The paleocatena identified within this time-slice also provides additional paleoenvironmental and paleoclimatic data, coinciding with the first hominin migrations out of Africa at ~1.8 Ma.
NoteIncludes bibliographical references
Noteby Emily Jane Beverly
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.