J. R. Bowman J. R. O’Neil T.E. Cerling 1988 <p><span>Stable isotopic analyses of Plio-Pleistocene and modern sediments in the fluvial-lacustrine system occupying the Turkana Basin, East Africa provide constraints on the paleoenvironmental and diagenetic histories of the Pliocene through the Recent sediments in the basin. The&nbsp;</span><i>δ</i>¹³<span>C values for carbonates in lacustrine sediments range from −15 to +22‰ relative to PDB, depending on the varying proportions of CO</span>₂<span>&nbsp;from the atmospheric reservoir and from various metabolic sources. The&nbsp;</span><i>δ</i>¹⁸<span>O values of carbonates in lacustrine sediments indicate that the isotopic composition of paleolake water varied by over 10‰ from the Pliocene to the present. The&nbsp;</span><i>δ</i>¹³<span>C values for pedogenic carbonates record paleoccologic variations and suggest that C</span>₄<span>&nbsp;plants did not become well established in the preserved depositional parts of the basin until about 1.8 myr ago. The&nbsp;</span><i>δ</i>¹⁸<span>O values pedogenic carbonates suggest a range of over 10‰ for the isotopic composition of soil water during this interval. They also suggest a period of major climatic instability from about 3.4 to 3.1 myr and at about 1.8 myr. Together, the&nbsp;</span><i>δ</i>¹³<span>C and&nbsp;</span><i>δ</i>¹⁸<span>O values of pedogenic carbonates indicate that the present conditions are as arid and hot as any that had prevailed during deposition of these Plio-Pleistocene sediments.</span></p> application/pdf 10.1016/0031-0182(88)90104-6 en Elsevier An isotopic study of a fluvial-lacustrine sequence: The Plio-Pleistocene koobi fora sequence, East Africa article