Date of Award

4-30-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Daniel M. Deocampo

Second Advisor

W. Crawford Elliott

Third Advisor

Lawrence Kiage

Fourth Advisor

Robin W. Renaut

Abstract

The Olorgesailie Drilling Project (ODP) and Hominin Sites and Paleolakes Drilling Project (HSPDP) targeted sites in the East African Rift Valley for their archeological and geological significance. The ODP team collected cores from the Koora Graben and the HSPDP team from Lake Magadi. To compliment these projects, we collected samples throughout southern Kenya to identify weathering patterns and potential mineral reactions to trace geologic processes between geologic sources and the hydrologic sump of Lake Magadi.

Mineralogical and geochemical analyses of the ODP and HSPDP cores suggest a similar paleoclimatic history over the past ~1.0 Myr: long-term aridification and intensifying climate variability over the past ~200-350 kyr. The paleolakes that occupied the Magadi and Koora Graben basins began as freshwater lakes at ~1.0 Ma. The mineralogy and geochemistry of the Magadi basin changed ~350 ka. The paleolake that occupied the Koora Graben experienced dessication at ~250 ka following thick volcanic ash and pumice deposition that preceded highly variable environmental conditions. Nearly all volcanic deposits recognized in the Olorgesailie cores have been zeolitized in the Magadi cores, but we assume that equivalent deposits were similar in thickness to the ODP cores. Trona deposits began to accumulate by ~100 ka, signaling intense aridification.

Mineralogical and geochemical analyses of surface and outcrop samples displayed unique characteristics associated with four distinct regions: the highlands to the north; the central area between Koora and Magadi; the greater Magadi basin in the south; and the Nguruman Escarpment to the west. Zeolitic alteration is common throughout southern Kenya. The most common zeolites in outcrop and surface samples are erionite and chabazite, which commonly occur in weathered tuffs and soils. Analcime was not present in any surface or outcrop sample, but is abundant in all cores, suggesting it forms in concentrated brines in lacustrine environments or proximal to lake basins near alkaline springs. The mineralogy and geochemistry of the ODP cores suggest the geologic source for material in the Koora Graben is primarily to the north, whereas the Magadi mineralogy suggests both western and central sources; however, much of the mineralogy reflects processes that occur within the basin itself.

Share

COinS