T187 Paleoclimate and Biotic Change in Africa, Mesozoic to the Present

Monday, 28 October 2013
1:00 PM - 5:00 PM
Room 605

PLANT WAX BIOMARKERS IN FLUVIAL-LACUSTRINE SEDIMENTS FROM EAST AFRICA:  PRESERVATION, ABUNDANCE, AND FEASIBILITY FOR PALEOCLIMATE RECONSTRUCTIONS

Paper number: T187-13
Program: Technical Sessions
Time: 4:10 PM – 4:25 PM

Authors

Abstract

A significant amount of the research on paleoclimate in eastern Africa is aimed at understanding the effects of climate change on vegetation and fauna. Stable carbon and hydrogen isotopes in leaf wax biomarkers are an emerging technique that could improve our understanding of vegetation and hydroclimate. Presently, no comprehensive biomarker data exist from terrestrial sediments of late Miocene to late Pleistocene age in eastern Africa. Fluvial-lacustrine deposits in the Omo-Turkana and Awash Basins contain a diverse faunal record that is rich in hominin taxa. A biomarker record from these deposits is an untapped source of paleoclimate data. Isotopic data from biomarkers could provide continuous, high-resolution terrestrial paleoclimate records that would enable direct comparison of climate and biotic change through time, fill gaps in the discontinuous isotopic record from paleosol carbonates, and compliment other existing geochemical and faunal records.

The heterogeneity of fluvial-lacustrine deposits requires assessment of biomarker preservation and abundance prior to generating isotopic records for paleoenvironmental reconstructions. We analyzed fluvial-lacustrine samples from the Omo-Turkana and Awash Basins to assess the feasibility of generating continuous isotopic records of vegetation and hydroclimate. We measured the distribution, abundance, and where possible, preliminary δD and δ13C values in n-alkanes and n‑alkanoic acids. The carbon preference index, which serves as an indicator for biomarker preservation, suggests suitable preservation in most samples. Abundances vary significantly in both n-alkanes and n‑alkanoic acids, with higher biomarker concentrations in lacustrine versus fluvial samples. About two-thirds of samples can be analyzed for δD values, whereas nearly all can be analyzed for δ13C values based on minimum analytical requirements. In many n-alkane samples, a large unresolved complex mixture is present, which can interfere with isotopic measurement unless further steps are taken to clean up the sample. Our results indicate fluvial-lacustrine deposits are promising biomarker archives, but illustrate careful screening and assessment are necessary.