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The AAPG/Datapages Combined Publications Database

Williston Basin Symposium

Abstract

SKGS-AAPG

Sixth International Williston Basin Symposium, October 7, 1991 (SP11)

Pages 165 - 178

DEPOSITIONAL HISTORY OF THE JURASSIC SYSTEM AND HYDROCARBON ACCUMULATIONS IN THE WAPELLA-MOOSOMIN AREA, SOUTHEASTERN SASKATCHEWAN

L.K. KREIS, Saskatchewan Energy and Mines, 201 Dewdney Avenue East, Regina, Saskatchewan, S4N 4G3

ABSTRACT

The Triassic/Jurassic section of southeastern Saskatchewan is an unconformity bounded sequence between the Mississippian subcrop and the Cretaceous Mannville Formation. Four lithostratigraphic units are recognized in the Jurassic of southeastern Saskatchewan: the Watrous, Gravelbourg, Red Jacket and Rierdon formations. The Red Jacket is the facies equivalent to strata between the lower member of the Gravelbourg and the Rierdon Formation.

The Triassic/Jurassic(?) red beds of the lower member of the Watrous Formation represent the earliest post-Mississippian deposits in the study area. They appear to have been laid down in a restricted marine environment but with repeated exposure, oxidization, and reworking. This phase was followed in the Bajocian by less restricted marine deposition, represented by anhydrites, dolomites and dolomitic mudstones of the upper member of the Watrous Formation and dolomitic limestones (unit A) of the lower member of the Gravelbourg Formation. Interbedded clastics and carbonates (Unit B) of the lower Gravelbourg Formation were deposited in a near-normal marine environment. In contrast, clastics and subordinate carbonates of the succeeding Red Jacket Formation were deposited during the Bajocian and Bathonian in depositional environments ranging from freshwater to brackish-water to open marine. This variation was probably caused by minor yet frequent fluctuations in sea level, causing broad shifts in the depositional environments. The unstable period of Red Jacket deposition was followed by a major marine transgression and shales of the Rierdon Formation were laid down in the study area during the Bathonian to Callovian.

Most Jurassic hydrocarbon production in southeast Saskatchewan is from the Rocanville and Moosomin members of the Red Jacket Formation in the Wapella-Moosomin area. Oil shows are also in the lower member of the Gravelbourg Formation; however, only one well is presently producing from this unit.

The dissolution of salt beds from the Middle Devonian Prairie Formation appears to have played a significant role in the depositional and hydrocarbon accumulation history of the Wapella-Moosomin area.

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