Global and Regional Impacts of Orbital Cycles on the Climate and Sedimentation of Icehouse and Greenhouse Worlds

Thomas L. Moore¹, Martin A. Perlmutter², and Christopher R. Scotese^3
1 Argonne National Laboratory, Argonne, IL
² Texaco, Inc, Houston, TX
³ University of Texas, Arlington, Arlington,

The Cenomanian/Turonian has been interpreted as a greenhouse world; a time with high atmospheric CO2 and no significant glaciation. In contrast, the Sakmarian has been interpreted as an icehouse world; a time with low atmospheric CO2 and major glaciation. These “end-member” conditions were not invariant. Milankovitch cycles produced climate changes throughout both these periods. To determine how climates varied, we used the Fast Ocean/Atmosphere Model (FOAM) at Argonne National Laboratory.

Insolation extremes occur during periods of high eccentricity combined with the effects of precession, which can generate the highest summer and lowest winter insolation cases, and high obliquity, which can cause the greatest insolation contrast between summer and winter. To evaluate these effects on climate, simulations were run for each end member; one using a precession value placing the northern hemisphere closest to the sun in the summer, and one placing the northern hemisphere farthest from the sun in the summer.

The model results showed: (1) interaction of eccentricity and precession is responsible for most climate variation; obliquity being responsible for far less change; (2) eccentricity and precession cause the northern and southern hemisphere climates to be out of phase; (3) within hemispheres, some regions demonstrate large climate changes while others remain stable; (4) climate changes related to Milankovitch cyclicity occur in both greenhouse and icehouse worlds; and (5) climate related processes such as weathering, erosion, sedimentation and deposition will be strongly affected by changes in orbital patterns, as well.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005