The Beaufort-Mackenzie Basin was initiated due to the Early Jurassic opening of the Amerasia Basin (Arctic Ocean) and developed into the foreland of the North American Cordilleran orogen during the Late Cretaceous and Tertiary. These geodynamic events sustainably deformed the crust while providing accommodation space for locally more than 16 km of Mesozoic-Cenozoic sediments.
To develop consistent crust-scale 3D structural models of the entire basin (391*251 km²), we integrate diverse datasets including seismic reflection and refraction profiles, well logs, and gravity data. The sub-sedimentary crystalline continental crust spans from 42 km thick, unstretched domains in the south to thinned domains of less than 10 km thickness in the north, where it passes over to the oceanic crust of the Canada Basin. The Mesozoic-Cenozoic sedimentary part of the model comprises seven clastic units (predominantly sandy shales) of which the modelled thickness distributions reflect a north(east)ward shift of the main depocentres through time. At constant depth level, the units thus tend to be younger, more porous, and less dense towards the north.
Significant lateral variations in observed temperatures at the same depth raise the question on the main temperature-controlling factors. Based on the structural model, we calculate the 3D steady-state conductive thermal field, thereby integrating the base of the relic permafrost layer (i.e. the 0°C-isotherm) as well as public-domain temperature and thermal conductivity data. As a result of the computations and in agreement with the observations, temperatures are lowest at the southern margin of the basin, where the insulating effect of the low-conductive Mesozoic-Cenozoic sediments is missing. Farther north, where moderately thick continental crystalline crust produces considerable heat and a thick pile of sediments efficiently stores it, temperatures tend to be highest. Temperatures decrease again towards the northernmost distal parts of the basin, where thinned continental and oceanic crust produce less radiogenic heat. Furthermore, differences in the basin-wide shale-to-sand-ratios of the sedimentary units and associated differences in thermal conductivity explain the observed trends of decreasing temperatures from the western to the eastern basin. Borehole locations showing larger deviations of the purely conductive model from temperature observations point to a locally restricted coupling of heat transport to groundwater flow.
Sippel, J., Scheck-Wenderoth, M., Lewerenz, B., Kroeger, K.F., 2013. A crust-scale 3D structural model of the Beaufort-Mackenzie Basin (Arctic Canada) Tectonophysics 591, 30-51.
Sippel, J., Scheck-Wenderoth, M., Lewerenz, B., Klitzke, P., under review. Deep versus shallow controlling factors of the crustal thermal field – insights from 3D modelling of the Beaufort-Mackenzie Basin (Arctic Canada). Submitted to Basin Research.
Performed as part of the larger Program MOM (Methane On the Move; LINK) - a large international effort with partners from geological surveys, research institutes and universities). We thank Dr. D. Issler from the Geological Survey of Canada for inspiring discussions.