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The AAPG/Datapages Combined Publications Database

CSPG Bulletin

Abstract


Bulletin of Canadian Petroleum Geology
Vol. 31 (1983), No. 4. (December), Pages 205-212

Cardium Formation 1. "Cardium, A Turbidity Current Deposit" (Beach, 1955): A Brief History of Ideas

Roger G. Walker

ABSTRACT

In 1953, oil was discovered in the Cardium Formation at Pembina, Alberta. It became important to determine Cardium depositional environments, and in 1955 F.K. Beach wrote a short paper entitled "Cardium, a turbidity current deposit." At the time the turbidity current hypothesis was only five years old. Turbidites were associated with mobile, geosynclinal belts, and few people in Calgary seemed willing to accept Beach's suggestion for the Cardium. Other suggestions in 1955 included that of Parsons, who proposed deposition "very near to the wave base." There were written discussions in 1956 and 1957, and a Cardium Symposium in 1957 at which there seemed to be little support for the turbidity current idea. As the science of sedimentology matured, especially with more work on recent sediments and sedimentary structures, the interpretations of the Cardium converged toward what by 1969 was a shoreline/tidal-flat/barrier-bar consensus. Since 1975-76, however, storm deposits have attracted considerable attention, and Cardium interpretations have begun to "deepen" again. It has recently been proposed that both conglomerates and sandstones represent offshore storm deposits, but this raises the question of how the sand was transported offshore.

In recent studies of the Ricinus, Previous HitCarolineNext Hit and Garrington fields, it is shown that water depths based on foraminiferal ecology may have been greater than 50 m. Cores of the Cardium show graded bedding in sands and gravels; beds with abrupt bases; sedimentary structures in sequence -- massive, parallel lamination, ripple cross-lamination (Bouma ABC and BC sequences); and a background sedimentation of bioturbated mudstone. There is no angle-of-repose cross bedding (scale 10 cm or greater) to suggest reworking at the depositional site. These features are best interpreted as formed by turbidity currents, although storm rip currents and wind-forced currents are also briefly discussed. In most outcrops and many cores, the only preserved sedimentary structure is hummocky cross stratification, believed to be formed by storm waves which, it is suggested, have modified the deposits of the turbidity currents. The balance of evidence, however, suggests that F.K. Beach (1955) was largely correct: the Cardium sandstones are turbidity current deposits (largely storm-modified), at least in the Ricinus-Previous HitCarolineNext Hit-Garrington area.

LA FORMATION CARDIUM 1. "LA CARDIUM, UN DEPOT DE COURANT DE TURBIDITE" (BEACH 1955): UNE HISTOIRE SOMMAIRE D'IDEES

RESUME

En 1953 le petrole fut trouve dans la formation Cardium a Pembina en Alberta. Il devint important par consequent de determiner les milieux de depot de cette formation, et en 1955 F.K. Beach ecrit une courte etude intitulee "La Cardium, un depot de courant de turbidite." On debattait l'hypothese du courant de turbidite depuis seulement cinq ans a cette epoque-la. Les turbidites etaient associees a des ceintures mobiles geosynclinales, et peu de personnes a Calgary etaient pretes a accepter l'hypothese de Beach pour la Cardium. En 1955 il y avait d'autres hypotheses: Parsons affirmait que le depot eut lieu "a proximite de la base de la vague." En 1956 et en 1957 il y eurent des discussions ecrites et en 1957 une conference sur la Cardium eut lieu. Toutefois il n'y avait pas beaucoup d'appui pour l'idee du courant de turbidite. Peu a peu, comme la science de la sedimentologie se raffinait, surtout a mesure que l'on etudiait les sediments actuels et les structures sedimentaires, les etudiants de la Cardium s'accordaient a croire en 1969 que la formation etait composee de cote / vasiere intertidale / barre cotiere. Cependant, depuis 1975-76, les depots de tempete ont attire beaucoup d'interet, et les interpretations de la Cardium ont commence a "s'approfondir" de nouveau. L'on a recemment suggere que les conglomerats et les gres proviennent de depots de tempete marins, mais cette hypothese pose la question suivante: comment le sable a-t-il ete transporte au large des cotes?

Des etudes recentes des champs Ricinus-Previous HitCarolineNext Hit-Garrington montrent que les tranches d'eau, basees sur l'ecologie foraminferale, ont pu etre plus profondes de 50 m. Des carottes de la Cardium revelent une sedimentation graduee dans les sables et les graviers, des lits avec des bases vives, des structures sedimentaires en serie -- massive / stratification parallele / stratification entrecroisee (les successions Bouma ABC et BC), et une sedimentation de fond composee de pelite fouie. Il n'y a pas d'angle de talus naturel dans la stratification croisee (d'une echelle de 10 cm ou de plus) qui suggerait du remaniement dans le lieu meme de depot. Ces caracteres sont mieux expliques comme formes par des courants de turbidite bien que l'on mentionne les courants sagittals de tempetes et les courants forces par le vent. La seule structure sedimentaire preservee dans beaucoup d'affleurements et nombreuses carottes est "hummocky cross stratification" -- que l'on croit forme par des raz-de-maree. Il est suggere que dans ces exemples, des tempetes ont modifiees les depots des courants de turbidite. Cependant, il reste a dire que la plupart de l'evidence prouve que F.K. Beach avait raison en grande mesure en 1955 -- les gres de la formation Cardium sont des depots de courant de turbidite (pour la plupart modifies par les tempetes) -- au moins dans les champs Ricinus-Previous HitCarolineTop-Garrington.

Traduit par Joan Lovell

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