ABSTRACT: Dating Dolomitization/Recrystallization Events Using Petrologic, Geochemical and Paleomagnetic Techniques
M. T. Cioppa, J. Lonnee, D.T.A. Symons, I. S. Al-Aasm, Earth Sciences, University of Windsor, Windsor, ON, Canada, and K. P. Gillen, Vox Terrae Int'l., Calgary, AB, Canada
The timing and origin of dolomitization in the Western Canada Sedimentary Basin has been controversial. Petrologic and geochemical analyses have been used to identify the relative timing of diagenetic phases and paleomagnetism to provide absolute ages in dolomitized hydrocarbon reservoirs in Devonian and Mississippian carbonates. By isolating the magnetization of a specific diagenetic phase, it can be dated. In the Late Devonian Sulphur Point Formation in the Rainbow South field five dolomitization events were identified. Detailed paleomagnetic analysis was completed on the fine crystalline (FCD), medium crystalline (MCD) and saddle (SD) dolomites and on the coarse and fine-grained limestone facies.
The magnetizations in the FCD and MCD were carried by pyrrhotite and magnetite of Late Jurassic and Late Cretaceous age, respectively, with preliminary paleopoles at N75degrees, E143degrees (dm, dp = 12 degrees, 14 degrees) and N71degrees, E193degrees (dm, dp = 8 degrees, 9 degrees). The SD magnetization was removed at magnetite blocking temperatures of > 320 degrees C and was Paleocene to Eocene in age, with a paleopole at N75degrees, E203degrees (dm, dp = 6 degrees, 6 degrees). In the limestones, the fine-grained mudstone facies carried a Late Devonian magnetization (N40degrees, E99degrees; dm, dp = 6 degrees, 12 degrees) whereas the coarser-grained packstones and grainstones carried a Cretaceous-Tertiary magnetization. The absolute ages determined from paleomagnetism agree with the relative timing of dolomite formation, determined using petrographic and geochemical techniques.
Search and Discovery Article #90907©2000 AAPG Eastern Section Meeting, London, Ontario, Canada