LAKE DISTRIBUTION IN THE EOCENE

Besides oceans, lakes can have a profound influence on climate patterns through atmosphere-water feedbacks via the ‘lake effect’. They serve as heat sinks and moisture sources that can affect intracontinental climates, as demonstrated by the Permian lakes in southern Gondwanaland or even the Great Lakes in North America. Lake distribution data from the geologic past will have considerable potential for testing and refining reconstructions of atmospheric paleocirculation as well as producing more accurate paleogeographic maps. According to both marine and terrestrial data, Eocene climate has been documented as the warmest period of the Cenozoic. In Eocene age sequences, lake deposits are associated with rift and thrust zones that are spread across North America, southeast Asia, Australia, and western Europe. The interrelationship between tectonics and the formation of lakes is well established; however, the reasons for the thermal maximum during the Eocene are still under debate. Proposed warming mechanisms include injection of metamorphic thermogenic and wetland methane, release of organically-derived carbon dioxide, poleward oceanic heat transfer, and reduction in the intensity of atmospheric circulation. Heat retention and transfer are important in all these mechanisms. Did the large number of lakes in the Eocene, as evidenced by their preserved deposits, add a ‘lake effect’ to the high global temperatures?

To address the lake effect problem in the Eocene, a paleogeographic map of lake distribution must first be generated. Data for approximately one hundred Eocene lake deposits were compiled through a literature search and use of the GGLAB database (Global Geological Record of Lake Basins). Information such as present location, relative age, and projected areal deposit extent (km2) were recorded along with citations. Time resolution of the lake deposits were separated out at the scale of the Lower, Middle, and Upper Eocene. Compiled data was plotted on Eocene maps of the PALEOMAP Project. Analysis of lake extent and distribution through the Eocene will follow.