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UBC Theses and Dissertations

Thermal maturation of the Western Canadian Sedimentary Basin in the Rocky Mountain foothills and plains of Alberta south of the Red Deer River England, Timothy David John


Vitrinite reflectance was measured for over 600 samples of coal and coaly particles from Jurassic to Paleocene strata in the Foreland Basin of southern Alberta, south of the Red Deer River, to establish a regional base of maturity data for modeling thermal history. The relationship between random and maximum reflectance for coals in the study area is: %RoR = 0.938 x %RoMax + .00112. Maturity of coal in strata of the same age generally increases from east to west across the Plains; however, significant variation in maturity is apparent in the Plains, possibly as a result of varying geothermal gradients. Maturity increases from south to north in the Disturbed Belt in the study area. Coalification gradients in the axis of the Basin are exceedingly low, averaging 0.07 log %RoR/km, a manifestation of very low paleogeothermal gradients resulting from rapid sediment deposition in the Paleogene. Time-averaged paleo-geothermal gradients for the deepest part of the Basin range from 7.5 to 15 deg. C./km based on measured coalification gradients. The thickness of eroded Tertiary section in the axis of the Basin is estimated to range from 5 to 9 km with an average value of about 6 to 7 km. Time-temperature modeling using an integral form of the Lopatin equation shows that for most of the Jura-Cretaceous wedge, the level of maturity required for hydrocarbon generation was not attained until the late Eocene. Syn- to post-orogenic maturation of strata in the Plains is a result of Basin loading by overthrust sheets or molasse. In the Disturbed Belt, a significant component of maturation resulted from overthrusting, as evident from maturity profiles of deep wells. A model describing the effect of overthrusting on maturity of footwall strata shows that paleo-geothermal gradients in the Disturbed Belt have been low, less than 20 deg. C./km, since Jurassic, and that thrust sheet thickness was probably 5 km or less in the Waterton, Highwood River (Foothills), and Jumping Pound areas, and greater than 5 km in the Highwood River (Front Ranges), and Burnt Timber Creek areas.

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