Sedimentology, Ichnology and High-Resolution Allostratigraphy of the Lower Cretaceous Viking Fonnation, Central Alberta, Canada

Abstract

<p> The Lower Cretaceous (Upper Albian) Viking Formation of central Alberta contains numerous linear sandbodies and fewer large irregularly-shaped sandbodies. Most studies to date have focused on individual sandbodies, leaving their interrelationships largely unknown. Developing a high-resolution allostratigraphy for the Viking of central Alberta allows mapping of regional bounding discontinuities and the definition of distinct allomembers. Placement of the Viking hydrocarbon fields within this framework permits an understanding of the exact stratigraphic relationships of the various fields. </p> <p> Examination of 120 cores and numerous well log correlations suggests the existence of four regionally mappable bounding discontinuities (BDl-4) which separate five distinct allomembers (I-V). Sandbodies within these allomembers were deposited in a variety of sedimentologically distinct environments. These include 'regional Viking' offshore to shoreface sandstones, prograding highstand shoreface sediments, transgressive incised shoreface sediments, and forced regressive, onlapping shoreface 'tongues'. The series of linear trending hydrocarbon fields from Joffre to Chain are also stratigraphically distinct. The sandbodies exist at five separate stratigraphic horizons and therefore are not all part of the same incised shoreface deposits. </p> <p> The four regional bounding discontinuities are interpreted as transgressive surfaces of erosion formed by four separate drops and subsequent rises of relative sea level. These fluctuations were greater than 30m and each complete cycle occurred over roughly 375,000 years. </p>