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.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California