Control of reservoir geometry and stratigraphic trapping by erosion surface E5 in the Pembina-Carrot Creek area, Upper Cretaceous Cardium Formation, Alberta, Canada

Seven major erosion (E) surfaces are found within the 100-m-thick Cardium Formation in the subsurface of Alberta. Erosion surface E5 has up to 20 m of erosional relief in the Carrot Creek area, and is cut into originally horizontal open-marine sandstones and mudstones. The E5 surface has been correlated into the Pembina area by construction of a structure map based on 2470 resistivity logs. The topography is interpreted to have formed during erosional shoreface retreat in a period of alternating transgression and still-stand of relative sea level. The erosion surface is overlain by a continuous veneer of conglomerate interpreted as a transgressive lag. The sandstones and mudstones below the erosion surface at Pembina shale out northeastward, partly forming a stratigraphic trap. These sediments are also truncated by the E5 erosion surface and buried by transgressive mudstones; these mudstones contribute significantly to updip stratigraphic trapping. The long, narrow sand body trends mapped in Pembina and adjacent fields are due to the erosive dissection of an originally extensive and continuous sheet of interbedded sandstones and mudstones, and not, as has been suggested, to an offshore bar origin for the fields. -from Authors