--> ABSTRACT: Deposition and Diagenesis of Frobisher Beds, Stoughton Area, Southeast Saskatchewan, by R. Louis Withers and Murray R. Nelson; #91033 (2010)

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Deposition and Diagenesis of Frobisher Beds, Stoughton Area, Southeast Saskatchewan

R. Louis Withers, Murray R. Nelson

The Mission Canyon Formation (Osagian) of the Stoughton area, southeast Saskatchewan, is composed of normal-marine, fossiliferous limestones (Alida beds), marine and terrestrial dolostones and sandstones (Kisbey Sandstone), and restricted marine limestones (Frobisher beds). Observations and interpretations of the oil-bearing Frobisher indicate that an island-shoal complex was initially formed under transgressive conditions. At most locations, the Frobisher is dominated by stacked coarsening-upward cycles 0.8-2.8 m thick, each consisting of varying proportions of lime mud, peloids, pisoids, and spherulitic oolites. Fenestral fabrics, algal structures, and root hairs are abundant in lower mudstones and wackestones. Interclastic fabrics are found in the upper packstones and rainstones. Microstalactites, mud-floored caverns, sheet pores, dissolution vugs, "eggshell" concretions, and pendant cements are more abundant toward cycle tops, and were formed during subaerial exposure due to meteoric-vadose diagenesis. All meteoric cements (bladed and equant calcite) are volumetrically less important than preceding stages of pore-filling fibrous calcite cementation. Fibrous oolite cementation and the paucity and low diversity of macrofauna within the rock matrix indicate a dominantly hypersaline regime during Frobisher deposition.

A synsedimentary (Osagian) origin of mineral formation, indicated by petrology, is also supported by Sr87/Sr86 isotope ratios. All measured values within and below the Frobisher limestone occur along the Early Mississippian seawater curve. Samples of the dolomitized and anhydritized Frobisher next to the Mississippian-Jurassic unconformity were not consistent with the seawater curve. Analogous rocks occur at the Haasard-Glenburn fields of North Dakota.

AAPG Search and Discovery Article #91033©1988 AAPG Rocky Mountain Section, Bismarck, North Dakota, 21-24 August 1988