Dr. Maitituerdi Aihemaiti 

Past Research

Depositional history of the Chala crater basin (Mt. Kilimanjaro, equatorial East Africa): insights from a high-resolution ~250 kyr paleoenvironmental archive 

Sediments on the bottom of Lake Chala, a 92 m deep crater lake on the border of Kenya and Tanzania near Mt. Kilimanjaro, contain a uniquely long and continuous record of past climate and environmental change in easternmost equatorial Africa. A 214.8 m long sediment sequence was obtained in November 2016 from Lake Chala, as part of an International Continental Scientific Drilling Program (ICDP) project. In this study, we use well log and core data combined with previously acquired high-resolution reflection seismic profiles to produce a detailed seismic stratigraphic architecture of the Lake Chala basin. Lake Chala sediments are finely laminated (varved) throughout most of the recovered sequence. All other sections display at least cm-scale lamination, demonstrating the persistence of a tranquil, profundal depositional environment throughout lake history. The sequence is occasionally interrupted by event deposits such as turbidites, up to 108 cm thick; as well as by multiple 2 to 9 mm thick visible tephra horizons and fish carcasses. 

Seismic stratigraphic analysis of Lake Chala's sedimentary infill allowed the identification of four major seismic units (U1, the oldest and U4, the youngest), each subject to distinctive hydrological and sedimentological processes due to fluctuating lake levels. The lowermost unit SU1 marks the start of the lake basin filling which is frequently interrupted by turbidite layers. Unit SU2 overlies unit SU1 and displays acoustically transparent and low amplitude reflections, which represents the start of sedimentation above volcanic ash cones. Unit SU3 is characterized by a thick package of ponding sedimentation under low lake levels which contributed to the development of a relatively flat unit SU4. Evidence for lake-level fluctuations in the drill cores includes major changes in saturated bulk density, natural gamma ray values, and total organic carbon. High lake-levels favor the preservation of organic matter through the development of anoxic conditions, while degradation of organic matter becomes more intense under low lake-level stages. Detailed correlation of core lithology and down-core logging data confirms that very high magnetic susceptibility values correspond to tephra layers, also variations in natural gamma ray values are closely related to internal lithological changes.