The Sedimentology, Stratigraphy and Depositional History of the Lower Cretaceous Viking Formation at Caroline and Garrington, Alberta, Canada

Abstract

<p>The Lower Cretaceous (Albian) Viking Formation at Caroline and Garrington, Alberta contains two regionally extensive erosion surfaces, VE3 and VE4, separating three allocyclic members, B/C, D, and E. These erosion surfaces, along with two possible correlative conformities at lower stratigraphic levels, can be mapped over large areas of the Alberta Basin allowing for the creation of a Viking Allostratigraphy.</p> <p>The basal allomember cored in the study area is informally termed B/C and is made up of burrowed siltstones deposited in an offshore marine setting. It is overlain by the regionally extensive ravinement surface VE3, which rises "steplike" towards the southwest. Allomember D, which overlies this unconformity, is composed of a shallowing upward succession of storm-dominated facies resulting from progradation of the shoreface towards the northeast. Allomember E is a complex succession of facies deposited over the regionally extensive ravinement surface VE4 during the final relative rise of the Boreal sea. Within Allomember E are up to six coarse grained, sheetlike beds sharply interbedded with marine shales. These interbeds are the result of basinward progradation of coarse sediment during periods of stillstand in the overall transgression, under the mixed influence of storms and tides. The coarse grained deposits originated at "steps" in the VE4 topography, representing successive positions of the retreating paleoshoreline, · and were swept basinward by. tides and storms over older, stratigraphically deeper "steps" and newly deposited shales. The coarse grained interbeds in Allomember E become thinner and finer in any one vertical section, reflecting the continued transgression of the shoreline towards the southwest.</p> <p>The boundaries of the Caroline and Garrington fields are determined by the extent of the sheetlike coarse grained deposits of Allomember E, and by the location of the postdepositionally determined oil-water contacts. Caroline and Garrington are producing from different stratigraphic intervals. caroline is producing from a shale-encased coarse grained interbed termed E3 (the Viking "A pool" of industry). At Garrington, this interbed is very thin, muddy and therefore unproductive. The Garrington field, in contrast, is producing from the stratigraphically lower coarse grained interval (VE4- CM2), which directly overlies the VE4 surface.</p>