Ichnology, sedimentology and stratigraphy of the Ostracode Zone, Bellshill Lake-Killam area, east central Alberta

Siliciclastic and carbonate facies from the Ostracode Zone were studied in detail in 45 cored wells, to complete the data 1640 geophysical well logs were analysed. The study area is located in the Bellshill Lake-Killam area of east central Alberta Twp. 39-44, Rng. 11W4-17W4. Hydrocarbons are produced from the Ostracode Zone in the Bellshill Lake, Thompson Lake and Forrestburg fields.;The Ostracode Zone contains a mixed siliciclastic-carbonate succession, consisting of 13 facies. These facies are arranged into 5 recurring facies associations. The Ostracode Zone consists of a regionally extensive succession (FA1 and FA4) and an incised valley succession (FA2, FA3 and FA5). The regional succession is comprised of storm influenced brackish bay, lacustrine and coal swamp environments. The valley fill succession is composed of point bar, bay and mud flat environments. The ichnology and sedimentology of the valley fill deposits demonstrate that the environment of deposition was subject to brackish water conditions, fluctuating salinities, and high sedimentation rates, indicating that the valley was occupied by an estuary during the deposition of the valley fill. The predominance of tidally generated features such as inclined heterolithic stratification and tidal flat deposits, among other features, indicate that the estuary that occupied the valley was tidally dominated.;The valley was incised in late Ostracode time (Late Aptian) during a relative lowstand of sealevel. In the study area, three subsequent, smaller lowstands resulted in the re-incision of the valley deposits and the development of a compound incised valley fill.