Implications of Post-Glacial Warming for Northern Hemisphere Heat Flow

摘要

Several observations lead us to suggest that the geothermal gradient in regions near the Pleistocene ice margin may contain a transient signal that causes significant underestimation of present day heat flow. Heat flow increases with depth in northern hemisphere periglacial regions in Eurasia and North America. Temperature gradients increase with depth in thick clastic rocks in the Williston Basin where compaction causes an increase in thermal conductivity. Thermally mature oil source rocks occur in the Williston Basin where subsidence history suggests that rocks should be immature unless paleo-heat flow was higher. Pollen analyses in upland lakes in southern Manitoba indicate that MJJA surface temperatures are 13 °C higher than they were 12,500 ka. Conductive heat flow models using the pollen temperature history as a forcing signal for surface temperature produce temperature vs. depth profiles with increasing gradients that are similar to profiles observed in the Williston Basin. The post-glacial warming signal appears to have been of the order of 10 to 15, thus northern hemisphere heat flow may have been underestimated by 30 to 60 percent depending on the depth of the original temperature gradient measurement. The implications for EGS in the northern hemisphere are that the resource may be at shallower depths than projected in recent studies.