Using Climate Model Experiments of Orbital Cycles to Understand Stratigraphic Variability

Moore, Thomas L.¹, Martin Perlmutter², Christopher Scotese³ (1) PaleoTerra, Bolingbrook, IL (2) Chevron, Houston, TX (3) PALEOMAP Project, Arlington, TX

Climate in general plays a role in the distribution of stratigraphic intervals, including reservoir and source rocks, by impacting sediment yield and productivity. However, climate is not static over the time interval these rocks form. Both long-term controls (such as continental geography) and short-term controls (such as orbital cycles or unique events) can all impact climate and deposition. Of these, the short-term controls are often the most difficult to assess because their effects are often below the time resolution of the strata.

We used the FOAM model to run multiple sets of orbital parameters to evaluate short-term change. The parameters chosen covered a range of obliquity, eccentricity, and precession states. From the results of modeling, we assessed (1) the impacts of orbital cycles on precipitation in river systems and upwelling and (2) the potential rate of variation through time. We concentrated on the Cretaceous (Cenomanian/Touronian) and the early Permian to evaluate two climatic extremes (hot and ice houses, respectively).

The results of modeling showed that (1) the interaction between eccentricity and precession generated the largest climate variation; (2) when eccentricity is high, relatively small changes in precession, 25% of a cycle (less than 5 kyr), can produce the largest differences; (3) the major atmospheric circulation cells can shift several degrees of latitude, impacting precipitation and wind patterns; and (4) environments such as deserts and rainforests vary in size and geographic range as circulation cells shift.

This work clearly demonstrates (1) the rate at which large paleoclimatic changes occurs is much faster than is commonly recognized and (2) the full range of high-frequency climate changes impacting an area need to be investigated when interpreting stratigraphy.