ABSTRACT

The Cardium Formation (Turonian, Upper Cretaceous) is predominantly marine and consists of interbedded sandstones and mudstones with some conglomerate. In the Garrington-Caroline area, about 100 km north-northwest of Calgary, the Cardium consists of two coarsening-upward sequences. These begin with dark mudstones, coarsen through various totally bioturbated facies, and terminate with more-or-less unbioturbated sandstones and conglomerates. The sandstones contain hummocky cross stratification (probably of storm origin) or the sequence of structures from parallel lamination upward into ripple cross-lamination (probably of turbidity current origin). There is no evidence of fairweather (tidal or longshore) currents, nor for reworking of the sands once they were emplaced into the basin.

The depositional site at Garrington and Caroline lay at least 100 km offshore, with southeasterly sediment dispersal from northwest of Pembina. Most foraminiferal assemblages in the mudstones associated with the Cardium sandstones indicate water depths greater than about 50 m.

A formal stratigraphic terminology is proposed. The "A sand" at Caroline can be traced on well logs to the "A sand" at Garrington -- this is termed the Raven River Member of the Cardium. Similarly, the "B sand" can be correlated between the two areas, and the sand body is termed the Burnstick Member. The mudstone that buries the Burnstick Member is black and massive, whereas the one that buries the Raven River Member is faintly silt-laminated and bioturbated. These mudstones form lithological markers that can be traced outside the immediate area of Caroline and Garrington fields, at least as far as Ricinus and possibly as far as Carrot Creek.

LA FORMATION CARDIUM NO. 3. LE SEDIMENTOLOGIE ET LA STRATIGRAPHIE DANS LA REGION DE GARRINGTON-CAROLINE, ALBERTA

RESUME

La formation Cardium (Turonien, Cretace superieur) est essentiellement marine et se compose de gres et argilites interstratifies ainsi que de quelque conglomerats. Dans la region de Garrington-Caroline, environ 100 km au nord-ouest de Calgary, le Cardium comprend deux sequences grano-croissantes. A la base, elles sont relativement non bioturbes. Les gres presentent une stratification entrecroissee de type "hummocky" vraisemblablement cause par des tempetes a l'origine, ou alors, la sequence consiste en laminations paralleles passant vers le haut a des laminations entrecroisees de type "ripple" attribuees a des courants de turbidite.

Il n'y a pas d'evidence de courants tranquilles (de marees ou cotiers), ni evidence de remaniement des sables, une fois deposes dans la bassin.

Le site de deposition de Garrington et Caroline devait etre situe au moins a 100 km de la cote. Les sediments s'epandaient alors en direction du sud-est provenant du nord-ouest de Pembina.

La plupart des assemblages de foraminiferes des horizons argileux associes aux du gres du Cardium indiquent une profondeur d'eau de plus de 50 m.

Une terminologie stratigraphique formelle est proposee, selon laquelle, le "sable A" a Caroline correle avec le "sable A" de Garrington sur la base des logs de forage reprondrait desormais au terme de membre Raven River du Cardium. De la meme maniere, le "sable B" correle entre les deux regions reprondrait au terme de membre Burnstick. La sequence argileuse qui recouvre le membre Burnstick est noire et massive alors que les argiles qui recouvrent le membre Raven River sont legerement laminees de silts et bioturbees. Ces series argileuses forment des marqueurs lithologique qui peuvent etre suivis au dela de la zone des champs de Caroline et de Garrington au moins aussi loin que Ricinus et meme jusqu'a Carrot Creek.