Evaluating
Paleoclimate Indicators Using Climate
Envelopes
Moore, Thomas L.1, Roy E.
Plotnick2, Martin Perlmutter3, Judith Totman Parrish4
(1) PaleoTerra, Bolingbrook, IL (2) University of Illinois at Chicago, Chicago,
IL (3) Chevron, Houston, TX (4) University of Idaho, Moscow, ID
A basic method in paleoclimate studies is
to infer climate
on the basis of the distribution of paleoclimate indicators,
such as evaporites and coals. Unlike many quantitative geochemical techniques
(such as using isotopes to yield temperatures), many indicators yield only
generalizations, such as “hot” or “wet.” These limited interpretations exist
because most sedimentary indicators represent non-unique
climate
conditions—that is, an indicator could represent a wide range of
climate
states. These simplifications present difficult problems when comparing
paleoindicators to modern climates or
climate
models or using models to predict
the distribution of sediments.
We present the concept of climate
envelopes to generate a more quantitative climatic interpretation of
sedimentary indicators. A
climate
envelope represents a calibrated range of two
or more
climate
-related parameters, such as temperature and precipitation, for
a particular sediment type, such as an evaporite. Unlike most approaches that
use annual averages, the envelope uses monthly averages because many indicators
do not form over the entire year. Envelopes can be expressed as
presence/absence distributions or as probability distributions. These
distributions can then be directly applied to
climate
data or
climate
model
results.
For this study, we focused primarily on
evaporites and histosols to evaluate the applicability of the climate
envelope
approach. We calibrated the indicators by using their modern distributions and
modern
climate
data and then applying the envelopes to Cretaceous and Permian
climate
simulations to predict indicator distributions.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California