25th International Meeting on Organic Geochemistry IMOG 2011

P-417
Contributions of δD analyses of plant-derived fatty acid methyl
esters in ravine deposits to understanding palaeoenvironmental
changes during the rise and fall of kingdoms in northern
Ethiopia
Valery Terwilliger 1,2,3 , Zewdu Eshetu 4 , Marcelo Alexandre 5 , Yongsong Huang 6 , Marilyn
Fogel 7
1 Institut des Sciences de la Terre d’Orléans (ISTO), Université d’Orléans, UMR 6113 du CNRS/INSU,
Université d’Orléans, Orléans, France, 2 Le STUDIUM/CNRS, Orléans, France, 3 University of Kansas,
Lawrence, United States of America, 4 Ethiopian Institute of Agricultural Research, Forestry Research Center,
Addis Ababa, Ethiopia, 5 Universidade Federal de Sergipe, São Cristóvão, Brazil, 6 Brown University,
Providence, United States of America, 7 Carnegie Institution of Washington, D. C., Washington, D. C., United
States of America (corresponding author:valery.terwilliger@cnrs-orleans.fr)
Knowledge of relationships between past
environmental changes and the rise and fall of
civilizations is contributing to strategies to best
manage today‘s environmental changes. The Tigrean
Plateau of northern Ethiopia and Eritrea has excellent
potential for the study of relationships between
environmental change and the rise and fall of
sophisticated societies. Nonetheless, the
palaeoenvironments of the region have been scarcely
studied and the reasons for the fall of even its most
powerful polity, Aksum, are the least understood of
the world‘s major ancient empires.
We are developing the potential of the Tigrean
Plateau to test a hypothesis that there are
generalizable relationships between environmental
(climate and land clearance in this study) changes
and the trajectories of civilizations. We have been
using stable hydrogen isotopic analyses of specific
plant-derived lipids because of their powerful potential
to record palaeoprecipitation as well as developing a
suite of soil chemical, macro and micromophological,
rockeval, and more rapid stable isotopic proxies for
past environmental characteristics.
We sampled 3 sections in each of 3 ravines in the
hinterlands of the earliest known kingdom (D‘MT) and
of the Aksumite Empire. Chronologies were achieved
from radiocarbon dating of charcoal [1]. Samples
were too low in alkanes for reliable δD analyses but
good records were obtained for plant-derived (≥ C26)
fatty acid methyl esters (FAMEs). The most abundant
FAME was hexacosanoic acid (C26) [2].
δDFAME C26 values were lower before 5600 cal yr BP
than after and this may indicate a shift from wetter to
drier climate. δDFAME C26 values tended to increase
implying continued drying until 1200 cal yr BP albeit
with significant periodic exceptions. Two exceptions
were declines in δDFAME and implied increases in
precipitation that corresponded to the rises of both
D‘MT and Aksum (Fig. 1). If effects of changes in C3
and C4 plant composition on the δD values are
accounted for, these increases in rainfall were higher.
Other proxies suggest that land clearance
dynamics were not similar between or within sites
during the times of the two polities. In conclusion,
climate had a more generalizable relationship to polity
trajectory than land clearance.
Fig. 1. Changes in proxy measurements during the times of
D‘MT and Aksum at one site.
References
[1] Gebru T. et al. 2009. Palaeogeography,
Palaeoclimatology, and Palaeoecology 282: 67-80.
[2] Courat, M. 2010. Rapport Master de Sciences de la
terre et environnement. Université d‘Orléans.
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