Thermal history of Canadian Williston basin from apatite fission-track thermochronology—implications for petroleum systems and geodynamic history K.G. Osadetz a, * , B.P. Kohn b , S. Feinstein c , P.B. O’Sullivan b,1 a Geological Survey of Canada, 3303 33rd St. NW, Calgary, Alberta, Canada T2L 2A7 b School of Earth Sciences, University of Melbourne, Melbourne, Victoria 3010, Australia c Department of Geological and Environmental Sciences, Ben Gurion University of the Negev, P.O. Box 653, Beer Sheva 84 120, Israel Received 21 July 2000; accepted 27 July 2001 Abstract Apatite fission track (AFT) thermochronology has been applied to a composite depth profile of Precambrian basement rocks underlying the Phanerozoic Canadian Williston Basin. Thermal histories derived from the AFT data record cycles of heating and cooling which follow the pattern of regional burial history, but which also indicate major temporal and geographic variations in the timing and degree of maximum Phanerozoic temperatures. These variations in the thermal history were not previously recognised from organic maturity indicators and subsidence models. Specifically, our study suggests a late Paleozoic heat flow anomaly with a geographic extent closer to that of Middle Devonian – Carboniferous Kaskaskia subsidence patterns than to that of the Williston Basin proper. This thermal anomaly has both economic and geodynamic significance. The recognition that potential Upper Cambrian – Lower Ordovician petroleum source rocks became fully mature during the late Paleozoic distinguishes that petroleum system from others that entered the main hydrocarbon generation stage in latest Cretaceous and Paleogene time. The late Paleozoic heat flow anomaly suggested from the AFT data implies a geodynamic coupling between inelastic Kaskaskia subsidence and previously inferred late Paleozoic lithospheric weakening. While the temporally varying heat flow model is preferred, the lack of independent constraints on the maximum thickness of upper Paleozoic strata precludes the outright rejection of the previous constant heat flow model. The AFT data provide important new constraints on the evolution of the epicratonic Williston Basin and its geodynamic models. Crown Copyright D 2002 Published by Elsevier Science B.V. All Rights Reserved. Keywords: Fission track thermochronology; Thermal history; Williston Basin; Petroleum systems; Geodynamics 1. Introduction The origin and evolution of epicratonic basins remain a significant geodynamic problem. Several early Paleozoic epicratonic basins including the North American Williston Basin (Fig. 1) exhibit geograph- ically persistent, symmetrical subsidence preserving relatively thin successions, up to about 5 km thick. This has led some workers to infer a single persistent subsidence mechanism (Ahern and Mrkvicka, 1984; Hamdani et al., 1994; Baird et al., 1995). Other features, including protracted subsidence, accelerated subsidence intervals and links to larger depositional 0040-1951/02/$ - see front matter Crown Copyright D 2002 Published by Elsevier Science B.V. All Rights Reserved. PII:S0040-1951(02)00055-0 * Corresponding author. Fax: +1-403-292-7159. E-mail address: kosadetz@nrcan.gc.can (K.G. Osadetz). 1 Present address: Department of Earth Sciences, Syracuse University, Syracuse, NY 13244-1070, USA. www.elsevier.com/locate/tecto Tectonophysics 349 (2002) 221– 249