--> Abstract: Controls on Paleosol Development in the Judy Creek Reef Complex, Upper Devonian Swan Hills Formation, West-Central Alberta, by Nancy Chow and Jack Wendte; #90039 (2005)

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Controls on Paleosol Development in the Judy Creek Reef Complex, Upper Devonian Swan Hills Formation, West-Central Alberta

Nancy Chow1 and Jack Wendte2
1 University of Manitoba, Winnipeg, MB
2 Geological Survey of Canada, Calgary, AB

Two major paleosol intervals occur in the Judy Creek reef complex which is a hydrocarbon-bearing isolated buildup of earliest Frasnian age in the subsurface of west-central Alberta. Comparison of these well-preserved paleosols enables evaluation of the influence of substrate lithology, the extent and duration of relative sea-level fall and the extent of erosion during transgression on paleosol development and preservation. The top of the lower paleosol corresponds to the R0.5 cycle contact which occurs near the middle of the lowermost megacycle identified in the Judy Creek reef complex. The R0.5 paleosol profile is up to 2 m thick and developed in peloidal-skeletal grainstone to stromatoporoid rudstone. It includes rhizoliths, green shale in thin beds and filling fractures, breccia, and pendant cements in solution vugs. Laminar calcrete is common throughout and glaebules, circumgranular cracks and microcrystalline dolomite are present locally. Lateral variations in the paleosol profile are mainly a function of erosion during the ensuing transgression.

The top of the upper paleosol is the R4 cycle contact at the top of the fourth megacycle. The R4 paleosol is hosted in peloidal mudstone to grainstone and is characterized by solution-enlarged subhorizontal fractures and small vugs filled by green shale, forming platy to blocky peds, which have been observed down to ~3 m below the R4 cycle contact. Laminar calcrete and green shale beds occur locally. Approximately 1-2 m of the paleosol profile is interpreted to have been removed during the ensuing transgression.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005