Stratigraphic architecture as a parasequence set and the genetic implications for the Cardium Fm. at Pembina
Creators: name: Joiner, Siegfried D.
Publisher: name: University of Calgary
Year: 1991
Subjects: subject: QE 651 J62 1991a
subject: Additional Copy: QE 651 J62 1991
subject: Geology, Stratigraphic
subject: Cardium Formation (Alta.)
subject: Geology - Alberta - Pembina region
subject: Paragenesis

description: Bibliography: p. 276-302.
description: The Pembina River Member of the Cardium Formation at Pembina is composed of a series of prograding and clinoforming parasequences which comprise the main sandstone reservoir units of the Pembina oilfield. All of the parasequences have similar sedimentologic characteristics which allow them to be recognized in core and on well logs. These 2 - 9 m thick parasequences display an upward increase in sandstone content, and an upward decrease in the amount of bioturbation. Well-developed parasequences show an upward change in ichnofossil assemblages from Cruziana / Zoophycos Ichnofacies to Skolithos Ichnofacies. A universal characteristic of parasequences is the abrupt marine flooding surface which truncates the top of the parasequence. Across this boundary, the sandstone content drops, bioturbation increases and hydrodynamic structures display smaller wavelengths. Frequently, strata immediately below the flooding surface are sideritized. Small transgressive lags of chert granules and uniquely textured interdigitating siderite nodules accumulate on some of these marine flooding surfaces and are an aid in correlating the parasequences from well to well. The parasequences were mapped using core and well logs and were shown to prograde and offlap to the southeast. They are interpreted to have formed during a period of relative sea-level fall. The parasequenes shale out in the direction of progradation, however this occurs gradually over a distance of 10 - 20 km. Individual parasequences can be traced as lobate bodies over an area of 1000 km2 . The parasequences are truncated on their updip edges by a major marine erosion surface. In the western and northeastern parts of the field, this transgressive erosion surface appears to bifurcate into two separate erosion iii surfaces. The transgressive surface marks the termination of sandstone deposition in the Pembina area. Both erosion surfaces underlie accumulations of conglomerate. In western Pembina, the older erosion surface underlies well sorted conglomerates and conglomeratic sandstones and mudstones which are interpreted to have formed in tidal channels during the earliest phases of transgression. In the central and eastern part of Pembina, the older erosion surface underlies bioturbated pebbly sandstones and mudstones which are interpreted to have formed in an open marine environment. The younger erosion surface underlies poorly sorted conglomerates which represent material winnowed from the underlying conglomerates. These younger conglomerates were reworked during the late phase of transgression. Subsurface members of the Cardium Formation at Pembina can be correlated to outcrop members using ammonites discovered in core and outcrop. For the first time, the Cardinal Member at Seebe, Alberta can be biostratigraphically correlated to the upper parts of the subsurface Pembina River Member at Pembina by the occurrence in both units of the Late Turonian ammonite Prionocyclus wyomingensis. The Leyland and Sturrock members at Seebe can now be positively dated by the discovery of the Early Coniacian ammonite Scaphites preventricosus.