Abstract
The Kimmeridgian/Tithonian (154.7−145.6 Ma) (middle and late Late Jurassic) was a time of expanded continental rifting, increased sea-floor spreading, and a relatively high eustatic sea level stand. These processes collectively caused the fragmentation and flooding of the megacontinent Pangea as well as the alteration of the global paleoclimate. Using a version of the Community Climate Model (CCM) from the National Center for Atmospheric Research, we report two Kimmeridgian/Tithonian paleoclimate seasonal simulations, with geologically inferred paleotopography: one using a CO 2 concentration of 280 ppm (pre-industrial level) and the other 1120 ppm. Increasing the CO 2 four-fold warms virtually the entire planet. The greatest warming occurs over the higher latitude oceans and the least over the equatorial and subtropical regions. Simulation of a warmer planet with an elevated greenhouse effect fits the distribution of paleoclimatically sensitive faunas, floras, and sedimentary rocks. Model results indicate that sea ice was restricted to the high latitudes of the Boreal and Austral seas, making landfall only in restricted areas. The trade winds bring heavy rainfall in December/January/February to eastern Gondwana and in June/July/August to the Tethys Sea margins. A strong June/July/August monsoon occurs over southeast Asia. The distribution of coals correlates to precipitation sufficient to maintain gymnosperm forests and coastal areas where water saturated sediments are a result of eustatic high stands of sea level. Evaporites are localized to areas of negative precipitation-evaporation. Runoff is restricted to regions of intense precipitation. Overall, the 1120 ppm CO 2 simulation provides a reasonable paleoclimate for the Kimmeridgian/Tithonian and provides a standard until a CCM with oceanic heat transport, a coupled atmospheric/oceanic model, or one with a finer grid cell configuration is available. The results need further scrutiny in areas with more detailed geologic information.
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