Abstract

In the Jenner-Suffield area, the informally named Ostracode Member (Aptian) is comprised of two distinct lithologies: a limy or laminated carbonaceous shale with a moderate amount of bioturbation and a very fine to fine grained clean sublitharenite sandstone. The basal carbonaceous and/or limy shale (facies 1) sits disconformably on the Ellerslie Member. This disconformity is marked by a flooding surface formed by the transgression of the Boreal Sea into low relief areas of southern Alberta and Montana forming a widespread shallow brackish water embayment. Sharply overlying these lower shales is a coarsening upward very fine to fine grained sublitharenite sandstone (Q:F:L ratio 86.1:0.7:13.2) which was deposited during a subsequent progradational phase. This laterally extensive barrier island deposit trends NNW for a known length of 104 km (65 miles), is on average 26 km in width (16 miles) with an average thickness of 9m (30 ft). This wave-dominated barrier is speculated to have been sourced from the northwest by the Cessford deltaic complex via longshore drift. Coastal plain sediments cap this barrier sequence, marking the infilling of the Ostracode basin.

Oilfields in the Ostracode sandstones are stratigraphic in nature. Traps are either formed by sand buildups flanked by non reservoir facies or by incision of younger tight upper Mannville valleys.