Provenance and Basin Geometry of Paleolake Olduvai Reconstructed using X-Ray Diffraction
Mentor 1
Lindsey McHenry
Start Date
10-5-2022 10:00 AM
Description
Olduvai Gorge, Tanzania is a well-known Pleistocene archeological site in a paleoanthropological setting of inter-fingering paleolake and volcanic fan deposits. This extensively-studied site provides abundant opportunities to reconstruct the paleoenvironments of early hominids including Homo habilis, Paranthopus boisei, and Homo sapiens. This project focuses on Upper Bed II of core 2A, one of four cores recovered in 2014 by the Olduvai Gorge Coring Project (OGCP). The position of the lake depocenter is expected to have shifted eastward during time of deposition of Upper Bed II which would have brought in more sediment from the west. Core 2A lies between the Fifth and FLK faults which follow the general southwest trend of the East African rift system. The section this study will focus on is at an interval of 30-36 meters below the surface, with an estimated age of `1.6 Ma. Samples were collected from core 2A in 32 cm intervals (from 16-18cm, 48-50cm, 80-83 cm, 112-114 cm, and 144-146 cm in each 1.5 m core segment where possible). A total of 14 samples were analyzed and interpreted using a Bruker D8 XRD, EVA pattern matching software, and the ICDD PDF-2 database. Analcime was found in every sample, indicating a highly saline-alkaline closed system environment, consistent published results for the underlying sediments. Quartz was found in eleven samples, and albite in six. These are likely detrital sediments from the Precambrian metamorphic quartzites and gneisses to the west. Diopside is found in one sample, anorthoclase in three, and titanite in two. These volcanic minerals likely come from the east as volcanic ash or fluvial/aeolian sediments from the adjacent Pleistocene Ngorongoro volcanic outcrops. These findings are consistent with an eastward changing lake depocenter, bringing in more sediment from the west, but that the highly saline-alkaline composition of the lake water remained constant.
Provenance and Basin Geometry of Paleolake Olduvai Reconstructed using X-Ray Diffraction
Olduvai Gorge, Tanzania is a well-known Pleistocene archeological site in a paleoanthropological setting of inter-fingering paleolake and volcanic fan deposits. This extensively-studied site provides abundant opportunities to reconstruct the paleoenvironments of early hominids including Homo habilis, Paranthopus boisei, and Homo sapiens. This project focuses on Upper Bed II of core 2A, one of four cores recovered in 2014 by the Olduvai Gorge Coring Project (OGCP). The position of the lake depocenter is expected to have shifted eastward during time of deposition of Upper Bed II which would have brought in more sediment from the west. Core 2A lies between the Fifth and FLK faults which follow the general southwest trend of the East African rift system. The section this study will focus on is at an interval of 30-36 meters below the surface, with an estimated age of `1.6 Ma. Samples were collected from core 2A in 32 cm intervals (from 16-18cm, 48-50cm, 80-83 cm, 112-114 cm, and 144-146 cm in each 1.5 m core segment where possible). A total of 14 samples were analyzed and interpreted using a Bruker D8 XRD, EVA pattern matching software, and the ICDD PDF-2 database. Analcime was found in every sample, indicating a highly saline-alkaline closed system environment, consistent published results for the underlying sediments. Quartz was found in eleven samples, and albite in six. These are likely detrital sediments from the Precambrian metamorphic quartzites and gneisses to the west. Diopside is found in one sample, anorthoclase in three, and titanite in two. These volcanic minerals likely come from the east as volcanic ash or fluvial/aeolian sediments from the adjacent Pleistocene Ngorongoro volcanic outcrops. These findings are consistent with an eastward changing lake depocenter, bringing in more sediment from the west, but that the highly saline-alkaline composition of the lake water remained constant.
