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.