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| Titel |
Chemical composition of modern and fossil hippopotamid teeth and implications for paleoenvironmental reconstructions and enamel formation – Part 2: Alkaline earth elements as tracers of watershed hydrochemistry and provenance |
| VerfasserIn |
G. Brügmann, J. Krause, T. C. Brachert, B. Stoll, U. Weis, O. Kullmer, I. Ssemmanda, D. F. Mertz |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 9, no. 11 ; Nr. 9, no. 11 (2012-11-26), S.4803-4817 |
| Datensatznummer |
250007413
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| Publikation (Nr.) |
 copernicus.org/bg-9-4803-2012.pdf |
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| Zusammenfassung |
This study demonstrates that alkaline earth elements in enamel of
hippopotamids, in particular Ba and Sr, are tracers for water provenance and
hydrochemistry in terrestrial settings. The studied specimens are permanent
premolar and molar teeth found in modern and fossil lacustrine sediments of
the Western Branch of the East African Rift system (Lake Kikorongo, Lake
Albert, and Lake Malawi) and from modern fluvial environments of the Nile
River.
Concentrations in enamel vary by two orders of magnitude for Ba (120–9336 μg g−1)
as well as for Sr (9–2150 μg g−1). The variations are
partially induced during post-mortem alteration and during amelogenesis, but
the major contribution originates ultimately from the variable water
chemistry in the habitats of the hippopotamids which is controlled by the
lithologies and weathering processes in the watershed areas. Amelogenesis
causes a distinct distribution of MgO, Ba and Sr in modern and fossil
enamel, in that element concentrations increase along profiles from the
outer rim towards the enamel–dentin junction by a factor of 1.3–1.9. These
elements are well correlated in single specimens, thus suggesting that their
distribution is determined by a common, single process, which can be
described by closed system Rayleigh crystallization of bioapatite in vivo.
Enamel from most hippopotamid specimens has Sr/Ca and Ba/Ca which are
typical for herbivores. However, Ba/Sr ranges from 0.1 to 3 and varies on
spatial and temporal scales. Thus, Sr concentrations and Ba/Sr in enamel
differentiate between habitats having basaltic mantle rocks or Archean
crustal rocks as the ultimate sources of Sr and Ba. This provenance signal
is modulated by climate change. In Miocene to Pleistocene enamel from the
Lake Albert region, Ba/Sr decreases systematically with time from 2 to 0.5.
This trend can be correlated with changes in climate from humid to arid, in
vegetation from C3 to C4 biomass as well as with increasing
evaporation of the lake water. The most plausible explanation is that Ba
mobility decreased with increasing aridification due to preferential
deposition with clay and Fe-oxide-hydroxide or barite on the watershed of
Lake Albert. |
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