Paper No. 210-2
Presentation Time: 1:45 PM
EARLY MIOCENE EVOLUTION OPEN ECOSYSTEMS AND C4 VEGETATION IN EQUATORIAL EAST AFRICA
PEPPE, Daniel J.1, COTE, Susanne2, DEINO, Alan L.3, DRIESE, Steven G.4, GARRETT, Nicole5, HILLIS, Kayla R.6, JACOBS, Bonnie F.7, JENKINS, Kirsten E.8, KINGSTON, John D.9, KINYANJUI, Rahab N.10, LEHMANN, Thomas11, LUKENS, William E.12, MCNULTY, Kieran P.13, MACLATCHY, Laura M.14, MICHEL, Lauren A.6, MILLER, Ellen15, NENGO, Isaiah16, NOVELLO, Alice17, OGINGA, Kennedy Ogonda18, ROSSIE, James B.19, STROMBERG, Caroline A.E.20 and UNO, Kevin T.21, (1)Terrestrial Paleoclimatology Research Group, Department of Geosciences, Baylor University, Waco, TX 76798, (2)Department of Anthropology and Archaeology, University of Calgary, Calgary, AB 2N 1N4, Canada, (3)Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, (4)Department of Geosciences, Baylor University, Waco, TX 76798, (5)Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, MN 55455-0219, (6)Department of Earth Sciences, Tennessee Tech University, Box 5062, Cookeville, TN 38505, (7)Huffington Dept. Earth Sciences, Southern Methodist University, PO Box 750395, Dallas, TX 75275, (8)Department of Sociology, Tacoma Community College, 6501 S 19th Street, Tacoma, WA 98466, (9)Department of Anthropology, University of Michigan, 101 West Hall, 1085 S. University Ave, Ann Arbor, MI 48109-1107, (10)Earth Sciences, National Museums of Kenya, P.O Box 40658-00100, Nairobi, 254, Kenya, (11)Messel Research and Mammalogy Department, Senckenberg Research Institute and Natural History Museum Frankfurt, Senckenberganlage 25, Frankfurt, 60325, Germany, (12)Department of Geology & Environmental Science, James Madison University, 801 Carrier Dr, Harrisonburg, VA 22807, (13)Department of Anthropology, University of Minnesota, 395 Hubert H. Humphrey Center, 301 19th Avenue South, Minneapolis, MN 55455, (14)Department of Anthropology, University of Michigan, Ann Arbor, MI 48109, (15)Department of Anthropology, Wake Forest University, Winston-Salem, NC 27106, (16)Department of Anthropology, Stony Brook University, Stony Brook, NY 11794-4364, (17)Biology Department, University of Washington, Seattle, 98195-3010, (18)Terrestrial Paleoclimatology Research Group, Department of Geosciences, Baylor University, One Bear Place, #97354, Waco, TX 76798, (19)Department of Anthropology, Stony Brook University, Stony Brook, NY 11794, (20)Department of Biology, University of Washington, 253 LSB, Box 351800, Seattle, WA 98195-1800, (21)Biology and Paleoenvironment, Lamont Doherty Earth Observatory, 61 Route 9W, PO Box 1000, Palisades, NY 10964-8000
While grasses are known from Africa since the latest Cretaceous, regional vegetation models suggest that equatorial Africa was predominantly forest, rather than grassland prior to the late Miocene. Pollen and stable isotope data suggest evidence for more open habitats and local occurrences of both C3 grasslands and C4 vegetation beginning in the middle Miocene ~15-13 Ma. By the late Miocene (~10 Ma), terrestrial stable isotopes from pedogenic carbonate and mammalian tooth enamel, as well as plant-wax isotopes from marine cores, show a major expansion of C4 grasslands across East Africa. Although these records provide some evidence for open-dry vegetation during the Cenozoic, the onset of open habitats with abundant C4 biomass is poorly constrained, and more detailed data sets are needed to assess local and regional vegetation patterns. With rich stratigraphic archives, the rift valleys of equatorial East Africa are an ideal setting to examine these questions. Here we present ecosystem and vegetation reconstructions from several early Miocene localities across Kenya and Uganda that span ~5.5 myr (~22-16.5 Ma), using paleosols, fossil leaves, phytoliths, and isotopic data from paleosol carbonates, bulk organics, and plant waxes. We use these data to assess spatial and temporal patterns of vegetation change, with a focus on the emergence of ecosystems containing C4 biomass. Quantitative and qualitative observations demonstrate significant spatial and temporal heterogeneity in vegetation through the early Miocene. Reconstructed biomes range from wooded grasslands with abundant C4 vegetation to closed canopy forests. Isotopic data and phytolith analyses independently confirm that C4 grasses were common at some of these localities. In particular, C4 biomass is most common at sites interpreted to be wooded grasslands, shrublands, and open woodlands. These data demonstrate that during the early Miocene, equatorial East Africa was a mixture of open to closed habitats, and that locally, open environments with C4 biomass were an important component of East African ecosystems >5 myr earlier than previously documented. Further, these results indicate that a variety of factors influenced C4 grassland evolution and their increasing dominance in African ecosystems through the Miocene.
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