Records from Lake Magadi, Kenya, suggest environmental variability due to changes in Earth’s orbit

Deocampo and his colleagues collect samples from the Lake Magadi drill core at the National Lacustrine Core Facility. Photo credit Hominin Sites and Paleolakes Drilling Project. Credit: Photo credit Hominin Sites and Paleolakes Drilling Project.

The Rift Valley lakes in East Africa range from freshwater systems to highly alkaline systems and are home to diverse ecosystems. These Rift Valley lakes are also sedimentary deposits, producing a high resolution environmental record that can be targeted to better understand the environmental and climatic context of human evolution over the last millions of years in Africa. East.

A new study published yesterday in Geology examines the geochemical record of drill core sediments collected from Lake Magadi, a saline and alkaline lake in Kenya‘s Southern Rift, which provides an almost million-year paleoenvironmental record of an unusual lake system of the Rift Valley.

Principal author Dan Deocampo of Georgia State University and a group of international co-authors drilled Lake Magadi as part of the Hominin and Paleolakes Site Drilling Project (HSPDP), which collected deep sediment core in the lake basins of the East African rift.

“We are trying to understand how the Earth’s surface environment has changed over the past millions of years and how this impacted early hominid habitats,” Deocampo said. “We are using many different proxies from ancient environments to understand how the environment has changed, how habitats have changed, and therefore how hazards and resources for early hominids have changed over time.”

Geochemical analysis of samples from Lake Magadi has shown some of the highest concentrations of elements like molybdenum, arsenic and vanadium ever reported in lake sediments. Hyperaccumulation of these elements has not been observed previously in other East African lakes and generally requires moiety conditions. Vesinic conditions occur when the lake water is both anoxic and sulphurous, usually triggered during negative water balance episodes such as droughts.

Records from Lake Magadi, Kenya, suggest environmental variability due to changes in Earth's orbit

Overview of Lake Magadi from the west shore. Photo credit Hominin Sites and Paleolakes Drilling Project. Credit: Hominin Sites and Paleolakes Drilling Project

“The amount of molybdenum accumulated in a sulphide-rich sediment in the lake is not going to tell us the structure of the habitat, where the hominids lived, but the fluctuations between these theminic conditions and the softer water conditions, which can tell us something about the pace of environmental change, ”Deocampo said.

Deocampo and his co-authors found thateuxinia became common after about 700,000 years and then tended to occur during intervals where the Earth’s orbit was more elliptical, which occurs over a cycle of 100. 000 years old. As the Earth’s orbit becomes more elliptical, the Earth can move away from the sun, causing greater variations in seasonal climate. Episodes of theminia provide an important indicator of intense droughts in the region during periods of extensive ice ages.

These large amplitude environmental fluctuations resulting in changes between the conditions in theminic and well-mixed lakes would have profoundly affected the availability of moisture and vegetation on evolving time scales.

Records from Lake Magadi, Kenya, suggest environmental variability due to changes in Earth's orbit

Collection of drill core at the Lake Magadi site. Photo credit Hominin Sites and Paleolakes Drilling Project. Credit: Photo credit Hominin Sites and Paleolakes Drilling Project.

The environmental variability suggested by the geochemical records of Lake Magadi is associated over time with the renewal of mammalian species and the first appearance of Middle Stone Age technology in the Southern Rift of Kenya between 500,000 years ago. and 320,000 years.

“Now it is a kind of point of contact with paleoanthropologists who are thinking about changes in the magnitude of environmental changes and how they relate to gene pool changes and changes in habitat structure, both first and foremost. latest appearances, ”Deocampo said.


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More information:
DM Deocampo et al, Orbital control of Pleistocene ellesinia in Lake Magadi, Kenya, Geology (2021). DOI: 10.1130 / G49140.1

Provided by the Geological Society of America


Quote: Records from Lake Magadi, Kenya suggest environmental variability caused by changes in Earth’s orbit (2021, September 21) retrieved September 21, 2021 from https://phys.org/news/2021 -09-lake-magadi-kenya-environmental- variability.html

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