ABSTRACT

The Virden member of the Lodgepole Formation (Mississippian) occurs in the subsurface of southwestern Manitoba and can be correlated over an area of approximately 1700 sq mi (4400 km²). Primarily a carbonate unit, the Virden member reaches a maximum thickness of approximately 80 ft (25m) and is an important producing horizon in several oil fields in Manitoba.

Study of nearly 2000 thin sections of core samples of the Virden member reveals that the original carbonate sediments have been modified by a number of diagenetic processes. These include: biological diagenesis, cementation, neomorphism, replacement, solution, dolomitization and anhydritization, and fracturing.

Biological diagenesis, glauconite replacement, calcite cementation, solution of aragonite shell debris and a number of neomorphic changes were relatively early diagenetic events. Stylolitization post-dates silicification of skeletal debris, hematite replacement, and some pyritization. Dolomitization, followed by the precipitation of void-filling and replacement anhydrite are late diagenetic, post-lithification events, related to the deposition of Middle Jurassic evaporites.