Development of a 36CI Chronology for Glaciations in Tropical East Africa

Abstract

A new glacial chronology for equatorial East Africa is developed using in-situ cos mogenic 36Cl measured in 122 boulders from moraines on Mount Kenya and Kilimanjaro. The oldest deposits sampled on Kilimanjaro yield a limiting 36Cl age of >360 calendar kyr (all 36Cl ages are in calendar years, cal. kyr or cal. yr). On Mount Kenya, the oldest moraines give ages of 355-420 kyr (Liki I) and 255-285 kyr (Teleki). Given the uncer tainty in our 36Cl ages, the Liki I moraine may correspond to either marine isotope stage 10 or 12, whereas the Teleki moraine correlates with stage 8. There is no evidence for stage 6 on either mountain. The Liki II moraines on Mount Kenya and moraines of the Fourth Glaciation on Kilimanjaro give ages of 28 ± 3 kyr and 20 ± 1 kyr, respectively. They represent the Last Glacial Maximum (LGM) and correlate with stage 2 of the marine isotope record. A series of smaller moraines above the LGM deposits record several read vances that occurred during the late glacial. On Mount Kenya, these deposits date to 14.6 ± 1.2 kyr (Liki IIA), 10.2 ± 0.5 kyr (Liki Ill), 8.6 ± 0.2 kyr (Liki IIIA) and -200 yr (Lewis); the corresponding deposits on Kilimanjaro have mean ages of 17.3 ± 2.9 kyr (Fourth Glaciation - Saddle), 15.8 ± 2.5 kyr (Little Glaciation -Saddle), and 13.8 ± 2.3 kyr (Fourth Glaciation - Kibo ). These data indicate that the climate of the tropics was extremely variable at the end of the last glacial cycle.