Paleogeography of Lake Turkana

What we think of as Lake Turkana has only been around for the past 200,000 years—the blink of an eye in geologic terms. The expanding and receding shores of the lake have provided food and water to organisms for millions of years.

Today, scientists study the stratigraphy—layers of rocks and sediment—of the Turkana basin to better understand the age of fossils discovered there. Stratigraphy also provides clues to the ancient paleoenvironments these organisms encountered when they were alive.

One of the earliest paleoenvironments of the Turkana basin was the Apak flood plain of the Pliocene epoch. Around 4.5 million years ago (mya), the ancestral Omo, Turkwell, and Keiro rivers joined to form the Turkana River. The Turkana is a “phantom river,” one scientists have never observed but is hypothesized to exist based on geologic and fossil evidence. For instance, the Turkana basin has yielded fossils of a whale and stingray, marine animals that have been known to swim upriver. This evidence suggests the “phantom” Turkana River may have had its mouth in the Indian Ocean.

Later in the Pliocene (about 4.1 mya), a large body of water, Lonyumun Lake, covered the Turkana basin for about 100,000 years. Lonyumun Lake drowned many terrestrial habitats, such as forests and grasslands. The remainders of these habitats existed on the margins of the basin. The chief fossils found during the time of Lonyumun Lake have been fish and mollusks.

Even later in the Pliocene (3.5 mya), a second body of water, Lokochot Lake, appeared and disappeared within 60,000 years. The most important fossil preserved by the sediments of Lokochot Lake is probably the extinct hominin Kenyanthropus platyops. K. platyops was related to human ancestors, and is important to the study of evolutionary patterns.

Mount Kulal, an active volcano, dominated the landscape of the Turkana basin about 2.4 million years ago, during the late Pliocene and early Pleistocene. In fact, fossils unearthed in the Tulu Bor flood plain, which blanked the basin near Mount Kulal, are embedded in tuff, or hardened volcanic ash.

Lorenyang Lake, a body of water formed during the Pleistocene (1.9 mya), was much longer-lasting than any other lake in the Turkana basin. Lorenyang Lake existed for about 400,000 years. Fossils of the Lorenyang Lake period are varied and rich, from hominins such as Homo habilis to organisms Homo habilis may have eaten: fish and shellfish, plants, and birds.

Lorenyang Lake eventually filled with sediment and was succeeded by another flood plain, the Chari flood plain (1.5 mya). Fossilized footprints in the Chari flood plain help provide scientists with evidence that at least some hominins were walking upright at this time.

The massive body of water that scientists call “Mega-Lake Turkana” emerged during the “African Humid Period,” about 9,000 years ago. The climate of the African Humid Period helped provide people with a rich array of resources: aquatic and wetland plant and animal species, a reliable source of freshwater, and “lush grasslands for hunters and fishers to utilize.”

Mega-Lake Turkana dried up almost completely about 7,500 years ago. The lake probably split into two small, shallow bodies of water. Scientists look at this period in Turkana basin’s history for a possible glimpse of how the landscape may be transformed if Ethiopia proceeds with the planned construction of a massive dam on the Omo River, the major tributary to Lake Turkana.