In the Countess Field, within the Mannville Group of strata, a series of shingled sandstone lenses with average dimensions of 8 km by 2 km by 20 m thick occur within a 50 to 55 m stratigraphic interval of interbedded sandstone and shale. This interval lies between a thin (<1 m) limestone marker below and a thin (1 to 2 m) coal seam marker above. The shingled lenses, which may coalesce to form either a linear or a tabular sandbody, are collectively referred to as the Glauconitic Sandstone, and exhibit the following six facies in the Countess Field:
Facies 1, gravelly, crossbedded, coarse grained sandstone interpreted as a tidal “strong current” facies. Facies 2, gravelly, parallel-bedded, coarse grained sandstone interpreted as a probable “storm” facies. Facies 3, medium grained, crossbedded, mud-draped sandstone with “bundle” sequences interpreted as a tidal “moderate current” facies. Facies 4, fine grained, flaser-bedded sandstone interpreted as a tidal “weak current” facies. Facies 5, wavy to lenticular-bedded, bioturbated, sandstone-shale alternations interpreted as “tidal flat” facies. Facies 6, wave-ripple-laminated or hummocky cross-stratified, fine grained sandstone interpreted as “storm” facies.
Palynological analysis of shale in Facies 5 yielded up to 11 species of open marine dinoflagellates. A tidal-delta-channel complex located within a wide-mouthed estuary that was migrating northwestward seems to be the most probable depositional model.
