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Abstract
Journal of Sedimentary Research, Section
A: Sedimentary Petrology and Processes
Vol. 66 (1996)No.
5. (September), Pages 948-955
Correlation of Cerium Anomalies with Indicators of Paleoenvironment
Kenneth G. Macleod (1), Anthony J. Irving (2)
ABSTRACT
Among 21 whole-rock samples of the Upper Cretaceous Niobrara Formation
from Colorado, the abundance of cerium relative to other rare earth elements
(Ce anomaly), the weight percent organic carbon (%Corg), and
the intensity of bioturbation all covary. This covariation is provocative
because %Corg and intensity of bioturbation track changes in
the concentration of oxygen in the local water column at the time of deposition
(Savrda and Bottjer 1989). Ce anomalies in apatite-rich fractions of the
Maastrichtian Zumaya-Algorta Formation from France and Spain and the Miocene
Monterey Formation from California show changes that also may coincide
with changes in ancient oxygen levels. Our results for the Niobrara samples
are the closest correspondence demonstrated betwe n paleo-redox conditions
and Ce anomalies, but we cannot yet determine whether the correspondence
reflects a cause-and-effect relationship. Variation in Ce anomalies is
influenced by a number of factors, including terrigenous input, depositional
environment, and diagenetic conditions. Potential interplay of these factors
prevents a unique interpretation of our whole-rock data; dissecting whole-rock
Ce anomalies through analysis of isolated sedimentary components, though,
is a promising avenue of research.
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